A fusible switch is usually mounted in an enclosure and incorporates an insulating base to carry an incoming line terminal for each phase. The circuit for each phase is completed through a pivotal knife blade which engages a corresponding contact stab and is electrically connected with a fuse clip having a fuse seated therein. In U.S. Pat. No. 4,302,648, commonly assigned to the Square D Company, a fusible switch is shown utilizing the above mentioned construction and which is hereby incorporated by reference.
Fusible switches are used in switchboards to distribute power for commercial and industrial applications. The need arises to distribute more power through enclosures which are the same size or smaller. This requires increasing the electrical rating of the switch to carry a higher voltage and current density while decreasing the size of the enclosure housing the electrical parts.
Among the problems caused by increasing the electrical rating of a switch is the heat emitted by the current carrying parts and the arc created by operating the switch. The parts can be damaged without proper ventilation of the switch and dissipation of the heat build-up.
Furthermore, the switch must be economical to manufacture. A switch with a higher electrical rating at comparable cost allows more widespread application. This also alleviates the problem of selecting an appropriate class of fuse.